1. Field of the Invention
Embodiments of the invention relate to a touch sensing device.
2. Discussion of the Related Art
User interface (UI) is configured so that people (users) are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technologies have continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc., and the touch UI has been basically installed in portable information devices. A touch screen is installed on a display element of household appliances or the portable information devices, so as to implement the touch UI.
A capacitive touch screen has durability and definition better than an existing resistive touch screen and is able to recognize a multi-touch input and a proximity touch input. Hence, the capacitive touch screen has the advantage of being able to be applied to various applications. Examples of the capacitive touch screen include a mutual capacitance touch screen using a mutual capacitance as a touch sensor and a self capacitance touch screen using a self capacitance as a touch sensor. As shown in FIG. 1, a self capacitance touch screen supplies a constant current to a self capacitance Cp until a voltage charged to the self capacitance Cp reaches a target voltage Vth, and turns on or off a switch SW in response to an output signal Fo of a comparator every predetermined period of time, so as to detect whether or not a touch operation is performed. Then, the self capacitance touch screen compares a time it takes for the voltage charged to the self capacitance Cp to reach the target voltage Vth with a previously determined critical value. As shown in FIG. 2, a time it takes for a charge voltage VCp of the self capacitance Cp to reach the target voltage Vth is counted according to oscillator clocks produced inside the self capacitance touch screen. The time required in the touch operation is longer than the time required in the non-touch operation. When the required time is equal to or greater than the critical value, the self capacitance touch screen decides a currently sensed touch sensor as a touch sensor corresponding to a touch input position.
In the related art self capacitance touch screen, sensing sensitivity has to increase so as to increase the touch sensitivity a user feels and accurately recognize a touch input trace or a dragging trace. However, because the related art self capacitance touch screen necessarily requires counting clocks of a high frequency so as to improve the sensing sensitivity, power consumption increases. Furthermore, because the related art self capacitance touch screen may perform a sensing operation only once within a given period of time, a detection capacity of a finger capacitance less than the self capacitance is reduced.